Well I don't think they'll do more than six or so seasons - and they'll surely have a bunch fewer Forsaken, so would likely give Ishamael more involvement in things like the Black Tower plot. The way things are going, I wouldn't be surprised if they skip the Stone of Tear and Callandor entirely, or almost entirely - having Rand proclaim himself the Dragon Reborn to the world at Falme next episode, then moving to the Waste in season three and covering the key points of books four and five already. So no death for Ishamael, or at most a faked one, no reincarnation needed.